1. Field of the Invention
The present invention relates to a protective film forming method and apparatus for forming a protective film on a work surface of a workpiece such as a semiconductor wafer.
2. Description of the Related Art
As well known in the art, a semiconductor wafer having a plurality of devices such as ICs and LSIs arranged in a matrix on the front side of a semiconductor substrate such as a silicon substrate is fabricated in a semiconductor device fabrication process, wherein each device is formed as a laminate of an insulating film and a functional film. In such a semiconductor wafer, the devices are partitioned from each other by a plurality of division lines called streets preliminarily formed on the semiconductor substrate, and the semiconductor wafer is cut along these streets to produce the individual devices. Further, in an optical device wafer, the front side of a sapphire substrate or the like is partitioned into a plurality of regions by a plurality of crossing streets, and a gallium nitride compound semiconductor or the like is layered in each of these partitioned regions of the substrate to thereby form an optical device. Such an optical device wafer is divided along the streets into a plurality of optical devices such as light emitting diodes and laser diodes, which are widely used for electrical equipment.
As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the streets formed on the front side of the wafer, there has been proposed a method including the steps of applying a pulsed laser beam to the wafer along the streets to thereby form a plurality of laser processed grooves and next breaking the wafer along these laser processed grooves by using a mechanical breaking apparatus (see Japanese Patent Laid-open No. Hei 10-305420, for example).
Such laser processing has advantages over cutting such that a processing speed is higher and a wafer formed of a hard material such as sapphire can be processed relatively easily. However, when a laser beam is applied to the wafer along the streets, thermal energy is concentrated at a region irradiated with the laser beam, causing the generation of debris, and this debris may stick to the surface of the devices formed on the wafer, causing a degradation in quality of the devices.
To solve this problem due to the debris, there has been proposed a laser processing system including a protective film forming apparatus for forming a protective film of resin such as polyvinyl alcohol on the front side of a wafer, wherein a laser beam is applied through the protective film to the wafer. The protective film forming apparatus included in this laser processing system has a spinner table for holding the wafer thereon under suction, wherein a liquid resin such as polyvinyl alcohol is supplied to the center of the wafer as rotating the spinner table holding the wafer, thus performing spin coating of the liquid resin (see Japanese Patent Laid-open No. 2007-201178, for example).